Azo dyes are one of the synthetic dyes that are used in many textile industries. Adsorption is one of the most effective techniques for removal of dye-contaminated wastewater. In this work, efficiency of multiwalled carbon nanotubes (MWCNTs) as an adsorbent for removal of Acid Red 18 (azo-dye) from aqueous solution was determined. The parameters affecting the adsorption process such as contact time, pH, adsorbent dosage, and initial dye concentration were studied. Experimental results have shown by increasing the adsorbent dosage, the rate of dye removal was increased, but the amount of adsorbed dyes per mass unit of MWCNTs was declined. pH as one of the most important influencing factors on the adsorption process was evaluated. The best pH for adsorption process was acidic pH of about 3. To describe the equilibrium of adsorption, the Langmuir, Freundlich and Temkin isotherms were used. The Langmuir isotherm (R2=0.985) was the best fitted for experimental data with maximum adsorption capacity of 166.67 mg/g. A higher correlation value of the kinetic's model was observed close to pseudo second order (R2=0.999) compared to other kinetic models.